class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int left=0;
        int right=0;
        int ret=0;
        int hash[200];
        int n=s.size();
        while(right<n)
        {
            hash[s[right]]++;
            while(hash[s[right]]>1)
            {
                hash[s[left++]]--;
            }
            ret=max(ret,right-left+1);
            right++;
        }
        return ret;
    }
};
